The present invention relates to a warning device that makes backing up a vehicle easier and safer by warning the driver of the vehicle of obstacles with which the vehicle might collide if it continues its movement.
A warning device of this type is known under the Bosch brand name Parkpilot system. With this known system, distance sensors integrated into the rear bumper use ultrasonic pulses based on the echo sounding principle to detect any objects behind the vehicle. The sensor signals are analyzed in an analyzing and controlling device that calculates the distance of the nearest object detected. As soon as the calculation indicates the presence of an obstacle less than 1.2 meters away from the vehicle, the driver is warned in the form of an intermittent audio signal. The pause between individual tones of the signal becomes shorter as the vehicle approaches the obstacle, until the signal becomes a continuous tone at a distance of 30 cm. At the same time, the distance is displayed on a multicolor LED display mounted in the rear of the vehicle.
Such a system is effective in parking a vehicle, where the vehicle is usually moving at very low speeds and its stopping distance is usually negligible, and the driver is dependent on information about any possible obstacles that might be located even approximately in the direction of travel of his/her vehicle.
When backing at a high speed over a great distance, the effectiveness of this system is limited because the time available between the occurrence of a warning signal and collision with the obstacle is often too short to be able to avoid it.
Although it would be technically feasible to expand the range covered beyond the abovementioned 1.2 meter detection radius, this would result in detection and signaling of a multiplicity of objects that are irrelevant for backing the vehicle, for example, because they are too far away from the direction of vehicle travel to actually be an obstacle. The driver would find this superfluous information annoying.
Another warning system is described in the article by Neil D. Lerner et al. xe2x80x9cDriver Backing Behaviour Research Implications for Backup Warning Devicesxe2x80x9d (preprint) Transportation Research Board, 76th Annual Meeting, Jan. 12-16, 1997, Washington, D.C. This system is activated when the vehicle is shifted into reverse gear. One or more distance sensors detect objects at a distance of approximately one meter to ten meters behind the vehicle. A control unit analyzes the distance information and decides whether there is a risk of collision. The criterion for this is the time until reaching the object (time to collision (TTC). The study by Lerner has shown that with an intentional approach to an object by a driver, the TTC is normally more than two seconds. However, when the TTC is less than two seconds, there is a high probability that the driver has not seen the obstacle. Thus, there is an acoustic collision warning when the system calculates a TTC of less than 1.5 to 2 sec. The system detects the following information for determination of the TTC:
object distance and approximate object position,
speed of the object and the vehicle,
instantaneous vehicle acceleration or deceleration, and
steering angle.
Extending the collision warning range to distances of less than one meter is problematical, because the warning strategy can no longer be implemented appropriately here. Although the speeds occurring in the usual parking maneuvers are low, they change very rapidly, so that a calculation of TTC is subject to great inaccuracies. Thus, reliable warning of collisions is impossible at distances of less than one meter on the basis of the TTC criterion.
The warning device according to the present invention offers the advantage that it can be used appropriately in both the near range of the vehicle at distances of less than 1.5 meters as well as at a greater distance of up to approximately ten meters, and in both distance ranges it supplies the driver with warnings of any obstacles only when actually necessary. By producing different warning signals, depending on whether an obstacle is in the near range of the vehicle or at a greater distance from it, this ensures that the driver can properly interpret the perceived warning signal and react to it in an appropriate manner.
The radius of the near range may vary according to the model of the vehicle and the driver""s range of vision in the reverse direction; for example a radius of 1 to 1.5 meters, typically 1.2 meters is a good guideline value for the limit between the near and far range.
To inform the driver quantitatively about the estimated distance from an obstacle or the extent of the risk of collision, the warning signals may be intermittent signals whose period or pulse duty factor may vary according to the estimated distance or the estimated risk of collision. The warning signals may both be acoustic signals, for example. This permits the use of a joint loudspeaker or loudspeaker system as the warning signal element to produce both signals. The warning signals may also be visual, e.g., an arrangement of LEDs may be used as the warning signal element. For example, the number of LEDs activated may be used as a measure of the estimated distance, and the LEDs may flash with different periods or pulse duty factors to signal a risk of collision with an obstacle at a distance greater than the limit value.
The situation could occur where the warning device detects a risk of collision with an obstacle in the far range beyond the limit value, and consequently outputs the far range warning signal until the time of occurrence of the obstacle in the near range below the limit value. In such a case, the far range warning signal should still be generated even when the obstacle has entered the near range, because if the far range warning signal were to stop suddenly, even if the near range warning signal were to begin to sound at the same time, this could mislead the driver to think that the risk of collision causing the warning signal has been eliminated. Therefore, the present invention advantageously provides for the analyzing and controlling device to continue output of the far range warning signal by the signal element in such a case. The far range warning signal stops only when it is estimated that there is no longer a risk of collision, e.g., because the vehicle has been braked to a sufficient extent or the direction of travel has changed or the obstacle has left the detection range of the sensor.
To avoid annoying the driver with a long-lasting near range warning signal, a switch is provided in a further embodiment of the present invention for blocking output of the near range warning signal. The analyzing and controlling device is equipped to cancel the block as soon as the estimate indicates that the obstacle is no longer in the near range, i.e., the distance from the obstacle is greater than the limit value. This embodiment of the analyzing and controlling device ensures that the near range warning signal will be triggered each time an obstacle enters the near range, even if the switch has been activated with an earlier backing maneuver.
According to another advantageous embodiment of the present invention, the warning device is equipped to detect the direction of an obstacle and it includes a plurality of similar warning signal elements which are distributed in the vehicle and are controlled as a function of the direction detected to indicate this direction to the driver. This makes it possible for the driver to perceive directly the direction into which the driver must steer to avoid the obstacle even if the obstacle is out of sight, e.g., because it is too low and is already too close to the vehicle.
Depending on the distance range to be detected, different sensors may be used to detect obstacles. A sensor used for detection in the near range should have a broad horizontal detection characteristic to be able to detect obstacles located beyond of the current path of the vehicle, whereas a sensor provided for detecting obstacles in the far range should have a narrower horizontal detection characteristic for detection of obstacles essentially only in the direction of vehicle travel. Primarily, ultrasonic sensors are used as the sensors for the near range; for example ultrasonic sensors, lidar or radar sensors may be used for greater distances.